The periodically poled ferroelectric wafer is a two-dimensional phononic superlattice. The important applications of such a solid include ultrasonic transducers at the micro/nano-scale for low intensity ultra-sonography, ferroelectric data storage, and development of very high frequency chips for next generation communication and information technologies, and others. In this work, we show theoretically and experimentally that a ferroelectric phononic superlattice has two distinctive resonances in acousto-electric transformation. They are associated with a split acoustic mode at the boundary between the first and second acoustic Brillouin zone.